Human milk is considered the ‘golden standard’ for infant nutrition. Processing animal milk, for example cow's milk, to more resemble the composition of human milk is known in the art as ‘humanizing’ animal milk. The process of humanizing animal milk involves changing the ratio of casein:whey proteins as found in animal milk (e.g. approximately 80:20 for cow's milk) to the desired ratio for infant nutrition as found in human milk, for example between 75:25 and 30:70, or usually approximately 40/60, which is the ratio found in human milk in months 0-6 post-partem. In addition, the mineral content of animal milk is typically higher than the content found in human milk. Thus humanization of animal milk also involves reducing of the mineral content. Preparation of products suitable for use in infant nutrition typically involves blending of various individually purified components in the appropriate ratios, either wet or dry. Current manufacturing processes require multiple dairy ingredients from intermediate suppliers, including skim milk or a concentrate thereof, including skim milk powder, demineralised whey or a concentrate thereof, including demineralised whey powder, whey protein concentrates or isolates, normally as powders, and pure grade lactose, typically in powder form, to formulate a nutritionally balanced infant formula.
WO 96/08155 describes a process for treating skim milk for the manufacture of cheese and milk powders, wherein whey proteins are removed from skim milk by microfiltration (MF) and ultrafiltration (UF). Volume concentration factors of 20-100 are employed in the UF step. No recombination of the MF retentate and UF permeate is described for the preparation of infant formulae and no attention is given to the concentration of minerals and trace elements such as phosphorus.
U.S. Pat. No. 5,503,865 discloses a process for treating skim milk, comprising microfiltration or ultrafiltration. The permeate thereof may be demineralised by for example ion exchange and/or electrodialysis in order to make the skim milk product suitable to be used in infant formulae. No combination of filtration techniques is disclosed.
WO 2008/127104 discloses the production of whey protein serum comprising residual beta casein by subjecting cow's milk to microfiltration over a membrane with a pore size of 0.3-0.5 micrometer at a temperature from 10-20° C., optionally with a further concentration step. The enlarged porosity gives rise to undesirably high casein content in the whey stream.
The process of U.S. Pat. No. 5,169,666 uses even lower temperatures (4° C.) at which the microfiltration over membranes with a pore size of 0.1-0.2 micrometer is performed. At this temperature significant amounts of (beta-)casein dissociates from the casein micelles and ends up in the MF permeate. Apart from being undesirably high in casein, the MF permeate is also too high in ash to be suitable for use in infant formulae. No measures are described to further reduce the ash content.
EP 1133238 describes a process wherein animal milk is subjected to microfiltration through a membrane having a porosity of 0.1-0.2 micrometer, after which the MF permeate is demineralised by electrodialysis. The mineral content of the electrodialyzed MF permeate is very low, and subsequent fortification with minerals and trace elements is required to obtain an infant formula.
WO 2009/059266 describes a process for preparing casein from skim milk by microfiltration, using a MF membrane having a porosity of 20-200 kDa and a VCF of 5-6. UF of the MF permeate may be used to separate the whey protein fraction into α-lactalbumin and β-lactoglobulin.
WO 2013/068653 describes a process for treating skim milk for the manufacture of infant formula bases, comprising MF of milk and UF of the MF permeate. Volume concentration factors of 2-10 are employed in the MF step and of 10-80 in the UF step. The lactose containing UF permeate is subjected to nanofiltration (NF) and used without further mineral removal steps in the preparation of infant formula bases. Although not recognized by the authors, such process would give rise to a final product which has unacceptably high mineral content, in particular too much divalent ions, as those do not permeate the NF membrane. This is reflected in the exemplary infant formulae disclosed in tables 2-7 of WO 2013/068563, which all have an ash content of 0.34 wt % or higher, based on final liquid product, which is undesirably high.
There is a need in the art for a process that enables efficient and cost-effective preparation of infant nutritional products from animal skim milk, which circumvents the above-mentioned drawbacks, in particular with respect to cost demanding demineralization and drying steps and the mineral content of the final product.